1. Field of the Invention
The present invention relates to a common mode choke coil and a high-frequency electronic device including the common mode choke coil.
2. Description of the Related Art
In the past, in a high-speed interface such as a universal serial bus (USB) or a high definition multimedia interface (HDMI), there has been used a differential transmission method where signals whose phases differ by 180 degrees are transmitted using a pair of signal lines. In the differential transmission method, a radiation noise and an exogenous noise are cancelled out by a balanced line. Therefore, the differential transmission method is insusceptible to these noises. However, in a signal line for a high-speed interface, from a practical perspective, a noise current of a common mode based on the asymmetry property of the signal lines occurs. Therefore, a common mode choke coil that suppresses such a common mode noise is used.
Usually, as described in Japanese Unexamined Patent Application Publication No. 2003-068528 or Japanese Unexamined Patent Application Publication No. 2008-098625, the common mode choke coil is configured as a small-sized stacked type chip component including two coils (a primary coil and a secondary coil) wound in a same direction. The primary coil and the secondary coil are symmetrically arranged parallel to each other in a stacking direction within a multilayer body.
However, in such a common mode choke coil, the primary coil and the secondary coil are arranged to overlap with each other in the stacking direction. Therefore, owing to a problem in a manufacturing process (a position displacement, a stacking displacement, or the like of a coil) or a structural problem (when being mounted in a printed wiring board, a coupling amount between each coil and the ground of the printed wiring board is different), a symmetry property is lost. If the symmetry property of the primary coil and the secondary coil is lost, a removal capability for the common mode noise is reduced.
On the other hand, in a common mode choke coil of the related art, in many cases, a magnetic substance is used as a multilayer body. However, since the magnetic substance has a relatively large frequency characteristic, in particular a loss of a normal mode signal in a high-frequency band is likely to become large. In addition, in a case where a sufficient coupling value is not obtained between the primary coil and the secondary coil, the loss of the normal mode signal is likely to become large.